I am trying to remember a story where the older girl character is sick with something that needs a operation to save her life and she keeps it from her friend who is a boy she refuses to date due to her illness she eventually tells him and he goes to the hospital to see her but gets there to late. I thought it was Aroslav's LNDtH. But it's not so I'm hoping someone here remembers better then me.
A Do-Over, Charlie Foxtrot's A New Past. The girl is Wendy, but the MC refers to her as Abby Normal. She appears in Ch.3, and checks out in Ch.4, having a tumour in her chest removed.
"I'm going to be in Bloomington, in the hospital," she managed to get out before I felt the tears drip on me.
I was at a loss. I stroked her back and hair and waited for her to calm down. "It's alright, Wendy. It will be alright," I kept repeating.
Eventually, she regained her composure. "I wanted to tell you tonight, since I have to start talking to teachers on Monday. I wanted you to hear it from me instead of your mother. It's the reason I can't let you be my boyfriend, even though I've thought of you that way for the past couple of weeks. This is serious."
ETA: Eventually I got to the other identically-named question posting, where this had already been answered. Oops.
Abby Normal
A pun of AB-Normal, since it sounds so similar to 'abnormal'. I always love a good play on words.
It's a do over story, and when the boy comes back, he resolves to go see his friend in the hospital before she dies. She pushed him away the first time because she didn't want people remembering her as all sickly, and the first time through he let her. The scenario I remember is that she had some kind of cancer, maybe leukemia, but was in remission for some time. Then the cancer came back. I think the author might also have written "Dance of a Lifetime".
I recall the story you're thinking of, and yeah, it was leukemia she suffered from (one of the less severe cancers, though still deadly).
The story I was referring to is "Rewind" by Don Lockwood, who is a fantastic author. It is incomplete, as are several of his stories, but they are VERY worth reading.
It can't be https://storiesonline.net/s/42289/rewind because
the older girl character is sick with something that needs a operation to save her life
That part absolutely does not fit. As you indicated, she has Leukaemia but all of the treatment options have been exhausted. That girl (Beth) was based on someone "Don Lockwood" knew when he was that age, and she died in that hospital. The final chapter of https://storiesonline.net/s/40599/naked-in-school-michelles-story supplies some more details.
possibly
'A Game of Inches' by Rhiannon57
https://storiesonline.net/library/storyInfo.php?id=21034